Direct measurement of polaron binding energy in AMnO₃ as a function of the A site ionic size by photoinduced IR absorption

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Photoinduced IR absorption was measured in undoped (LaMn)₁₋δO₃ and (NdMn)₁₋δO₃. We observe broadening and a 44% increase of the midinfrared anti-Jahn-Teller polaron peak energy when La³⁺ is replaced with smaller Nd³⁺. The absence of any concurent large frequency shifts of the observed PI phonon bleaching peaks and the Brillouin-zone-center internal perovskite phonon modes measured by Raman and infrared spectroscopy indicate that the polaron peak energy shift is mainly a consequence of an increase of the electron phonon coupling constant with decreasing ionic radius <rₐ> on the perovskite A site. This indicates that the dynamical lattice effects strongly contribute to the electronic band narrowing with decreasing <rₐ> in doped giant magnetoresistance manganites.